Medical imaging devices provide non-invasive methods to visualize the internal structure of a patient. Such non-invasive visualization methods can be helpful in treating patients for various ailments. For example, the early detection of cancer in a patient can be important in treating that patient. For most cancers, when detected at an early stage, the survival probability of the patient can increase.
There are many medical imaging methods available for visualizing the internal structure of a patient, each with its own benefits and its own limitations. For example, non-invasive medical imaging techniques may include MRI systems, three-dimensional (3D) X-ray computed tomography (CT) imagers, 3D optical coherence tomography imagers, or other 3D medical image of a tissue of a patient such as single proton emission computed tomography, and position emission tomography.
Magnetic resonance imaging (MRI) uses magnetic fields to image tissue of a patient placed inside a powerful uniform magnetic field of an MRI scanner. The MRI scanner can align the magnetic moments of protons in the tissue (typically hydrogen protons of water molecules in the tissue) in the direction of the field, processing about the field at their Larmor frequency. An excitation magnetic field (typically orthogonal to the main magnetic field) near the Larmor frequency is applied to alter the alignment of the protons in the tissue, typically flipping the magnetic moment of the protons in the main field. When the excitation field is turned off, the protons emit a photon that can be detected and processed to form an MRI image of the tissue. Each image is a slice of the tissue of the patient, and numerous images or slices are created that clearly show all the features of the tissue of the patient. The slices can be reconstructed into a single three-dimensional image, allowing complete visualization of the tissue of the patient scanned from all angles.
Other 3D imaging systems include tomosynthesis systems, which are X-ray based systems, and have recently been developed for use in breast cancer screening. In contrast to typical mammography systems, the tomosynthesis system acquires a series of x-ray projection images, each projection image obtained at a different angular displacement as the x-ray source traverses along a path over the breast. Reconstructed tomosynthesis slices reduce or eliminate the problems caused by tissue overlap and structure noise in single slice two-dimensional (2D) mammography imaging. Digital breast tomosynthesis also offers the possibility of reduced breast compression, improved diagnostic and screening accuracy, fewer recalls, and 3D lesion localization.
Ultrasound imaging is another non-invasive medical imaging technique, which uses sound waves, typically produced by piezoelectric transducers (or transducers) to image a tissue in a patient. The ultrasound transducer focuses the sound waves, typically producing an arc-shaped sound wave which travels into the body and is partially reflected from the layers between different tissues in the patient. The reflected sound wave is detected by the transducer and converted into electrical signals that can be processed by the ultrasound scanner to form an ultrasound image of the tissue. The ultrasound images formed may be 2D images or 3D images. The 3D ultrasound images may be formed by producing sound waves at different viewing angles, multiplexing the reflected signals and processing the multiplexed signals to construct a three dimensional scan image of a body object. In contrast with MRI and tomosynthesis systems, ultrasound systems typically produce a real-time stream of consecutive images.